You can mount images to already created templates.
To configure a new custom execution environment, you must first mount bootable storage media to a template in case you want to install an operating system.
To mount storage media to a created template:
On the Templates & Storage page, select the Templates tab.
Click the name of the template that you want to mount image to and select ISO image in one of the following ways:
On the Prepare image step, do the following:
Select the required image in the ISO image drop-down list or click the Upload image button and select the required ISO file.
Click the Proceed button.
On the Configure template step, select the required image in the drop-down list.